8 COM Spark Plugs

[Gannet]

Hugo,
I was surprised that the connection at the top was 'loose'. Although in the back of my mind was there not a device to improve the spark in HT leads by creating a gap? Anyway, whatever the theory, it does work and it certainly makes spark plug production with this kind of connection cheap and easy. Yes, I think it was fired as a complete assembly.


In respect of finding TDC, I use a hand held dial indicator gauge through the M18 threaded hole in the head. The probable accuracy and repeatability of this method is within +/- I.5 degree. The measurement method should depend on what accuracy one requires. To set the ignition timing on a FV or to measure the port timing, then getting TDC within 1.5 degrees is fine. Other errors will occur in measuring the actual timing of course. So how accurate does one really need to be?

Jeremy

[Keith.P]

I can honestly say, I have never had to set the timing on a seagull, even a rebuild, the previous mark left by the stator screw was always good enough.
With my FVP having a setting of 45 degrees BTDC, a degree or two isn't going to make much if any noticeable difference.
What is the timing setting anyway, do seagull say?

[Gannet]

Keith,
I think that you are dead right. Several degrees with an FV/FVP probably doesn't make any difference. The original ident mark on the FVs seems to vary enormously. I have seen 57 deg BTDC. I adjust all mine to 45deg, which is a nice round number and which seems to work well. It is probably not the optimum setting, but I am happy with it. All values are with the points set at 0.020.

Getting back to 8 COMs - I have now fitted them to all of my FVs, the older ones with the 8x32 UNC HT connection in conjunction with the Champion brown plug cap. The others have the M4x0.7 connection with the Seagull black plug cap. Thanks for encouraging me to fit these original spec (?) plugs. However if they perform unreliably, I know who to contact!

Jeremy

[Nudge]

Nudge, I would say that that is too flimsy to find TDC, i borrowed something similar to do my Marston timing and it was a M10 bolt threaded through the nut part of the plug.

I would have to agree 100% with what you are saying. But when I was having a look it was the only thing I had with an 18mm thread.
I was looking because I have 2 WS silvers and the timing was so different between them both I wanted to know why. (and I still don't know)!

[Charles uk]

It was probably a device like this that Seagull 101 was talking about.

It's an 18mm adjustable piston stop, which works in all Seagull cylinders that use an 18mm spark plug, & can be adjusted to stop the piston at around 90 degrees, when it's traveling at it's fastest, giving the best accuracy.

[Nudge]

Just a tad heaver than mine! I would have to be careful not to stuff that through the piston.

[Keith.P]

Charles, when you came around that time to debunk the idea of my FVP having a 45 degree of timing, didn't you say something about another was of setting up the TDC of the motor?

[Charles uk]

Yes but it only works on the Seagull models that don't have a deflector at the piston end of the inlet port.
So it should work on just about everything prior to 1967.

Remove spark plug & the carb, stick masking tape all around the circumference of the flywheel, fasten a pointer from 2 crankcase bolts with the point over the masking tape & wind the piston up to around TDC.

Slide the thickest feeler gauge that will fit in the inlet port so it almost touches the con rod, then rotate the flywheel until the piston skirt stops against the feeler gauge & mark the flywheel tape under the pointer, rotate the flywheel the other way till it stops & mark the tape.
Ensure the feeler gauge is flat against the skirt of the piston & not bending!

Measure the mid point of the 2 marks on the tape & mark, repeat on the other side of the flywheel, one of the midpoint marks will be TDC & the other BDC!